Specifies the style in which to draw the active element.
This must be one of dotbox (show a focus ring around the active element),
none (no special indication of active element) or underline (underline the active element).
The default is underline.

Specifies the reference of a variable.
The value of the variable is an array to be displayed inside the widget; if the variable value changes then the widget will automatically update itself to reflect the new value.
Attempts to assign a variable with an invalid list value to -listvariable will cause an error.
Attempts to unset a variable in use as a -listvariable will fail but will not generate an error.

Specifies one of several styles for manipulating the selection.
The value of the option may be arbitrary,
but the default bindings expect it to be either single,
browse,
multiple,
or extended; the default value is browse.

Specifies one of two states for the listbox: normal or disabled.
If the listbox is disabled then items may not be inserted or deleted,
items are drawn in the -disabledforeground color,
and selection cannot be modified and is not shown (though selection information is retained).

Specifies the desired width for the window in characters.
If the font doesn't have a uniform width then the width of the character ``0'' is used in translating from character units to screen units.
If zero or less,
then the desired width for the window is made just large enough to hold all the elements in the listbox.

The Listbox method creates a new window (given by the $widget argument) and makes it into a listbox widget.
Additional options,
described above,
may be specified on the command line or in the option database to configure aspects of the listbox such as its colors,
font,
text,
and relief.
The listbox command returns its $widget argument.
At the time this command is invoked,
there must not exist a window named $widget,
but $widget's parent must exist.

A listbox is a widget that displays a list of strings,
one per line.
When first created,
a new listbox has no elements.
Elements may be added or deleted using methods described below.
In addition,
one or more elements may be selected as described below.
If a listbox is exporting its selection (see exportSelection option),
then it will observe the standard X11 protocols for handling the selection.
Listbox selections are available as type STRING; the value of the selection will be the text of the selected elements,
with newlines separating the elements.

It is not necessary for all the elements to be displayed in the listbox window at once; commands described below may be used to change the view in the window.
Listboxes allow scrolling in both directions using the standard xScrollCommand and yScrollCommand options.
They also support scanning,
as described below.

The Listbox method creates a widget object.
This object supports the configure and cget methods described in Tk::options which can be used to enquire and modify the options described above.
The widget also inherits all the methods provided by the generic Tk::Widget class.

Sets the active element to the one indicated by index.
If index is outside the range of elements in the listbox then the closest element is activated.
The active element is drawn with an underline when the widget has the input focus,
and its index may be retrieved with the index active.

Returns a list of four numbers describing the bounding box of the text in the element given by index.
The first two elements of the list give the x and y coordinates of the upper-left corner of the screen area covered by the text (specified in pixels relative to the widget) and the last two elements give the width and height of the area,
in pixels.
If no part of the element given by index is visible on the screen,
or if index refers to a non-existent element,
then the result is an empty string; if the element is partially visible,
the result gives the full area of the element,
including any parts that are not visible.

Deletes one or more elements of the listbox.
First and last are indices specifying the first and last elements in the range to delete.
If last isn't specified it defaults to first,
i.e.
a single element is deleted.

If last is omitted,
returns the contents of the listbox element indicated by first,
or an empty string if first refers to a non-existent element.
If last is specified,
the command returns a list whose elements are all of the listbox elements between first and last,
inclusive.
Both first and last may have any of the standard forms for indices.

Query or modify the configuration options of an item in the listbox.
If no option is specified,
returns a list describing all of the available options for the item (see Tk_ConfigureInfo for information on the format of this list).
If option is specified with no value,
then the command returns a list describing the one named option (this list will be identical to the corresponding sublist of the value returned if no option is specified).
If one or more option-value pairs are specified,
then the command modifies the given widget option(s) to have the given value(s); in this case the command returns an empty string.
The following options are currently supported for items:

Records x and y and the current view in the listbox window; used in conjunction with later scan dragto commands.
Typically this command is associated with a mouse button press in the widget.
It returns an empty string.

This command computes the difference between its x and y arguments and the x and y arguments to the last scan mark command for the widget.
It then adjusts the view by 10 times the difference in coordinates.
This command is typically associated with mouse motion events in the widget,
to produce the effect of dragging the list at high speed through the window.
The return value is an empty string.

Adjust the view in the listbox so that the element given by index is visible.
If the element is already visible then the command has no effect; if the element is near one edge of the window then the listbox scrolls to bring the element into view at the edge; otherwise the listbox scrolls to center the element.

Sets the selection anchor to the element given by index.
If index refers to a non-existent element,
then the closest element is used.
The selection anchor is the end of the selection that is fixed while dragging out a selection with the mouse.
The index anchor may be used to refer to the anchor element.

Returns a list containing two elements.
Each element is a real fraction between 0 and 1; together they describe the horizontal span that is visible in the window.
For example,
if the first element is .2 and the second element is .6,
20% of the listbox's text is off-screen to the left,
the middle 40% is visible in the window,
and 40% of the text is off-screen to the right.
These are the same values passed to scrollbars via the -xscrollcommand option.

This command shifts the view in the window left or right according to number and what.
Number must be an integer.
What must be either units or pages or an abbreviation of one of these.
If what is units,
the view adjusts left or right by number character units (the width of the 0 character) on the display; if it is pages then the view adjusts by number screenfuls.
If number is negative then characters farther to the left become visible; if it is positive then characters farther to the right become visible.

Returns a list containing two elements,
both of which are real fractions between 0 and 1.
The first element gives the position of the listbox element at the top of the window,
relative to the listbox as a whole (0.5 means it is halfway through the listbox,
for example).
The second element gives the position of the listbox element just after the last one in the window,
relative to the listbox as a whole.
These are the same values passed to scrollbars via the -yscrollcommand option.

Adjusts the view in the window so that the element given by fraction appears at the top of the window.
Fraction is a fraction between 0 and 1; 0 indicates the first element in the listbox,
0.33 indicates the element one-third the way through the listbox,
and so on.

This command adjusts the view in the window up or down according to number and what.
Number must be an integer.
What must be either units or pages.
If what is units,
the view adjusts up or down by number lines; if it is pages then the view adjusts by number screenfuls.
If number is negative then earlier elements become visible; if it is positive then later elements become visible.

Tk automatically creates class bindings for listboxes that give them Motif-like behavior.
Much of the behavior of a listbox is determined by its selectMode option,
which selects one of four ways of dealing with the selection.

If the selection mode is single or browse,
at most one element can be selected in the listbox at once.
In both modes,
clicking button 1 on an element selects it and deselects any other selected item.
In browse mode it is also possible to drag the selection with button 1.

If the selection mode is multiple or extended,
any number of elements may be selected at once,
including discontiguous ranges.
In multiple mode,
clicking button 1 on an element toggles its selection state without affecting any other elements.
In extended mode,
pressing button 1 on an element selects it,
deselects everything else,
and sets the anchor to the element under the mouse; dragging the mouse with button 1 down extends the selection to include all the elements between the anchor and the element under the mouse,
inclusive.

Most people will probably want to use browse mode for single selections and extended mode for multiple selections; the other modes appear to be useful only in special situations.

Any time the selection changes in the listbox,
the virtual event <<ListboxSelect>> will be generated.
It is easiest to bind to this event to be made aware of any changes to listbox selection.

In addition to the above behavior,
the following additional behavior is defined by the default bindings:

In extended mode,
the selected range can be adjusted by pressing button 1 with the Shift key down: this modifies the selection to consist of the elements between the anchor and the element under the mouse,
inclusive.
The un-anchored end of this new selection can also be dragged with the button down.

In extended mode,
pressing button 1 with the Control key down starts a toggle operation: the anchor is set to the element under the mouse,
and its selection state is reversed.
The selection state of other elements isn't changed.
If the mouse is dragged with button 1 down,
then the selection state of all elements between the anchor and the element under the mouse is set to match that of the anchor element; the selection state of all other elements remains what it was before the toggle operation began.

If the mouse leaves the listbox window with button 1 down,
the window scrolls away from the mouse,
making information visible that used to be off-screen on the side of the mouse.
The scrolling continues until the mouse re-enters the window,
the button is released,
or the end of the listbox is reached.

If the Up or Down key is pressed,
the location cursor (active element) moves up or down one element.
If the selection mode is browse or extended then the new active element is also selected and all other elements are deselected.
In extended mode the new active element becomes the selection anchor.

In extended mode,
Shift-Up and Shift-Down move the location cursor (active element) up or down one element and also extend the selection to that element in a fashion similar to dragging with mouse button 1.

The Left and Right keys scroll the listbox view left and right by the width of the character 0.
Control-Left and Control-Right scroll the listbox view left and right by the width of the window.
Control-Prior and Control-Next also scroll left and right by the width of the window.

The delete function is implemented slightly differently from the standard array implementation. Instead of setting the element at that index to undef it instead physically removes it from the Listbox. This has the effect of changing the array indices, so for instance if you had a list on non-continuous indices you wish to remove from the Listbox you should reverse sort the list and then apply the delete function, e.g.

would safely remove indices 20, 12, 4, 2 and 1 from the Listbox without problems. It should also be noted that a similar warning applies to the splice function (which would normally be used in this context to perform the same job).

inserts @list as elements in an already existing listbox and selects the element at index 1, which is "b". If we then

print @$selected;

this will return the currently selected elements, in this case "b".

However, if the "ReturnType" arguement is passed when tying the Listbox to the scalar with value "index" then the indices of the selected elements will be returned instead of the elements themselves, ie in this case "1". This can be useful when manipulating both contents and selected elements in the Listbox at the same time.

Importantly, if a value "both" is given the scalar will not be tied to an array, but instead to a hash, with keys being the indices and values being the elements at those indices

You can also manipulate the selected items using the scalar. Equating the scalar to an array reference will select any elements that match elements in the Listbox, non-matching array items are ignored, e.g.

would insert the array @list into an already existing Listbox and select element at index 1, i.e. "b"

@array = ( "a", "b", "f" );
$selected = \@array;

would select elements "a", "b" and "f" in the Listbox.

Again, if the "index" we indicate we want to use indices in the options hash then the indices are use instead of elements, e.g.

@array = ( 0, 1, 5 );
$selected = \@array;

would have the same effect, selecting elements "a", "b" and "f" if the $selected variable was tied with %options = ( ReturnType => "index" ).

If we are returning "both", i.e. the tied scalar points to a hash, both key and value must match, e.g.

%hash = ( 0 => "a", 1 => "b", 5 => "f" );
$selected = \%hash;

would have the same effect as the previous examples.

It should be noted that, despite being a reference to an array (or possibly a has), you still can not copy the tied variable without it being untied, instead you must pass a reference to the tied scalar between subroutines.